"I've read the speech," he says, as he begins to once again mount a defence of his industry, and of Barclays in particular. Judging by the fluency of his delivery, Mr Varley has had plenty of practise recently.

The behaviour of banks has seldom been under greater scrutiny, and Barclays has had a torrid time since appointing Bob Diamond, the well-remunerated head of its investment banking arm, to succeed Mr Varley next Spring.

Vince Cable, the business secretary, has called investment banks "casinos", while George Osborne, to whom Mr Varley is said to be close, said earlier this year that Mr Diamond's bonus after the financial crisis "beggared belief".

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The latest dart from Mr King came in his speech to the Trade Unions' Congress. "There was nothing fair about the financial crisis. It was not caused by problems in the real economy; it came out of the financial sector [...] Our financial system needs radical reform," he said.

In many ways, given the enormous public and political pressure that has come in the wake of the financial crisis, it is no wonder that Mr Varley has chosen to exit Barclays.

Insiders say that the Warwick-born, Oxford-educated, career banker made it clear seven years ago, when he took the Barclays helm, that he would retire at 55. "And the last three years have not exactly been the easiest," one added.

Mr Varley has weathered the storm well, however, and manages to be both contrite about the financial crisis and spirited in defending the industry, and the 'universal' bank model of having both a retail and an investment banking arm.

"What I accept is that there are public policy issues here that should be debated," he says, adding that Barclays will "participate extensively" in the consultation being carried out by Sir John Vickers' independent banking commission.

"We have strong opinions on the subject," he says. "Our view is that the universal banking model acts as a source of risk diversification, not risk aggregation. If you look at the empirical evidence, and there is an extensive volume over the last three years, and over the last 100 years, I actually do not see a correlation between the failure of a bank and the particular shape of a bank. The defining characteristic of bank failure is weak risk management."

As the financial crisis erupted, Barclays adroitly managed to resist a government bail-out and Mr Varley notes that the bank reported profits at every reporting period from the summer of 2007 to 2010.

"Our business model and strategy have been extensively stress-tested both substantively by the crisis and virtually by our regulators," he says. "We generated aggregate profits over the financial crisis of £25bn and I think that is an indication of the resilience of the business model."

On that fateful weekend of October 11 and 12, 2008, when Lloyds-TSB, HBOS and the Royal Bank of Scotland were part-nationalised, rumours suggest that Mr Varley cannily chose to negotiate by telephone, rather than in person at the Treasury, a move that threw the government, which already had its hands full with the other banks, off-balance.

"I think the right way of thinking about it is over the relevant weekend, the FSA working with its tripartite colleagues formed a judgement about what capital ratios it wanted British banks to have," says Varley.

"In some cases British banks were required to declare they were taking money from the state if they were going to open on Monday morning and in some cases they weren't. In our case, as everybody else was, we were required to increase our capital ratios but we were given until June 2009 to increase our ratios as opposed to 48 hours.

"If you ask me: 'Did you go to Whitehall over the weekend to meet the Treasury?' the answer is: No I didn't, I sat in Canary Wharf surrounded by my team."

By avoiding the bail-out, Barclays has avoided much of the fury directed at the other banks for continuing to pay bonuses despite having taken taxpayer's money. After our interview, Mr Varley conceded at a financial conference in Shanghai that banks had to repay the taxpayer before they could win back trust.

However, he is steadfast on the issue of remuneration. "We understand the furore over bonuses," he says. "If the pay of teachers and nurses is being frozen, or cut, then we must be sensitive. At Barclays we only pay what we need to pay." He points out that the bonus pool at the bank in 2009 was 15pc of its costs. "When I tell this to clients, and ask them about their own businesses, they think this is reasonable," he says.

What will he do next? He has already been linked to HSBC and Aviva, but Mr Varley won't reveal his plans. Until next year, the focus is on a smooth transition of power, he says. "What Bob and I have got to ensure is that our colleagues in Barclays, all 150,000 of them, are not distracted." And with that, he is off, ready to face down another hostile audience and defend his industry once more.